Controllable transformation of CoNi-MOF-74 on Ni foam into hierarchical-porous Co(OH)2/Ni(OH)2 micro-rods with ultra-high specific surface area for energy storage

Abstract

Thanks to the rich porosity, high specific surface area and tunable components, MOFs-derived hydroxides have become outstanding electrode materials for supercapacitors. According to an ion etching/exchange reaction method, the self-sacrifice template of CoNi-MOF-74 micro-rods that anchored on Ni foam are controllably transformed into a series of composites of Co(OH)2/Ni(OH)2 with specific structure. They are nanoflakes-wrapped solid micro-rods (CoNi-2), nanoflakes self-assembled micro-rods (CoNi-6) and nanoflakes self-assembled micro-tubes (CoNi-12), respectively. Among them, the CoNi-2 demonstrates the largest BET surface area (208.8 m2/g) and the highest areal capacitance (16.3 F/cm2 at 2 mA/cm2), exhibiting the most promising electrochemical energy storage ability. A corresponding asymmetric supercapacitor (CoNi-2//AC) delivers high energy density of 0.5 mWh/cm2 at power density of 1.6 mW/cm2 and excellent cycling stability (86.6 % capacitance retention after 10 000 cycles at 50 mA/cm2). Moreover, an all-solid-state asymmetric supercapacitor successfully lighten a light-emitting diode (LED) for one minute, implying great potential for practical applications in energy storage.